With the rapid advancements in wireless communication systems, user equipment (a.k.a. terminal equipment) such as the mobile phone is playing a bigger role in people's life. In addition to its communication functions, other functions of the user equipment, e.g., accessing a WLAN (Wireless Local Area Network) by the user equipment, have been increasingly explored. Moreover, to facilitate the user equipment to implement communication links and data interchange with other apparatuses, IR (infrared), Bluetooth and USE interfaces are becoming part of a standard configuration of the user equipment. Especially, Bluetooth headphones are increasingly widely used. WLAN systems, Bluetooth systems, and the like all work at the ISM (Industrial, Scientific and Medical) bands. For example, as one of the commonly used ISM bands in the word, the band 2400 MHz-2483.5 MHz is also one of the most commonly used ISM bands.
When a user equipment communicates with another apparatus at a frequency band that is close to, or a multiple of, the frequency band at which the user equipment communicates with its corresponding base station, these two types of communication may interfere with each other. For example, a wireless communication system Long-Term Evolution (LTE) system is one of the systems beyond 3G (IMT-2000). An LTE system may work at many frequency bands according to the LTE series specification [36.101]. Of these frequency bands used by LTE, some are adjacent to the ISM bands, e.g., band 40 for LTE TDD (Time Division Duplex) system deployments: 2300 MHz-2400 MHz; band 7 for LTE FDD (Frequency Division Duplex) system deployments: 2500 MHz-2570 MHz (uplink), 2620 MHz-2670 MHz (downlink). Of these frequency bands used by LTE, some are a multiple of the frequency bands used by the GPS (Global Positioning System) system, e.g., band 13 for LTE FDD system deployments: 777 MHz-787 MHz (uplink), 746 MHz-756 MHz (downlink); and band 14 for LTE FDD system deployments: 788 MHz-798 MHz (uplink), 758 MHz-768 MHz (downlink). When an LTE user equipment works at one of the aforementioned frequency bands, if a WLAN system or a Bluetooth system on the user equipment is activated, then the LTE system and the ISM system (the WLAN system, the Bluetooth system, or the like) working at adjacent frequency bands in the user equipment may interfere with each other due to adjacent-band leakage, which may even result in a communication failure when the bit error rate is high. If a GPS system on the user equipment is started up at the same time, the GPS system may fail to function due to harmonic interferences from the LTE system.
A conventional method to solve the above problem is to employ a higher-performance transmission filter in the transmitting terminal on the user equipment for the communication with the base station, e.g., an LTE system, and/or in the transmitting terminal on the user equipment for the communication with another apparatus, e.g., an ISM system, to reduce adjacent-band leakage and/or harmonic interferences to the greatest extent possible. A disadvantage of this method is that it significantly increases the cost of the user equipment.